1. Field of the Invention
The present invention relates in general to self-referencing grating-based waveguide sensors (e.g., optical sensors) that are used to detect the occurrence of a bio-chemical interaction (e.g., biological binding of antigen-antibody pairs).
2. Description of Related Art
Grating-based waveguide optical sensors have been used in a wide variety of applications and devices including for example optical filters, laser cavity mirrors and biosensors. In the biosensing application, an optical interrogation system is used to monitor changes in the refractive index or variations in the optical response of the optical sensor as a biological substance is brought into a sensing region of the optical sensor. The presence of the biological substance alters the optical response of the optical sensor when it causes a bio-chemical interaction like material binding, adsorption etc. . . . This alteration of the optical response enables one to use the optical sensor to directly monitor biological events in label-free assays where the expense and experimental perturbations of fluorescent dyes are completely avoided. Unfortunately, in addition to enabling the detection of variations in the optical response due to an bio-chemical interaction, the optical sensor is sensitive to environmental conditions such as temperature, pressure and changes in the bulk refractive index of the buffer solution. The buffer solution is the fluid used to reference the start and end-point of sensing measurements before and after the introduction of the chemical or biological fluid which contains the biological substance that can cause the bio-chemical interaction. As such, there is a need for an optical sensor that is designed to be self-referencing so one can separate the effects of a bio-chemical interaction like a surface binding from changes in environmental conditions. This need and other needs are satisfied by the self-referencing optical sensors and methods of the present invention.